JP2015221517A - Method for producing ceramic discharge vessel - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a technique for producing a ceramic discharge vessel, which enables accurate adjustment of a firing shrinkage ratio without causing ill effects to properties as a luminous tube with a simple method.SOLUTION: The method for producing a ceramic discharge vessel comprises: a slurry forming step of mixing alumina, an auxiliary, and water to form a slurry; a binder addition step of adding a binder to the slurry; a casting step of filling the slurry, to which a binder has been added, into a gypsum mold, holding the same for a specified time, drying, and demolding to form a molded body; a preliminary firing step of preliminarily firing the molded body at a relatively low temperature; and a main firing step of firing the preliminarily fired body formed in the preliminary firing step at a high temperature of 1600°C or more. The binder addition step includes a step of determining a binder content corresponding to a desired firing shrinkage ratio from a calibration curve showing a pre-determined relationship between the binder content and the firing shrinkage ratio.

Description

  The present invention relates to a method for manufacturing a ceramic discharge vessel for a high-pressure discharge lamp, and more particularly to a technique for adjusting firing shrinkage.

  In recent years, high-pressure discharge lamps used in discharge containers made of translucent ceramics (hereinafter referred to as translucent ceramics) have been widely used instead of quartz discharge containers (arc tubes). Since translucent ceramics are superior in heat resistance and corrosion resistance compared to quartz, a high-pressure discharge lamp using the ceramics can obtain very excellent characteristics such as high efficiency, high color rendering, and long life. .

  In general, a ceramic discharge vessel manufacturing process includes a step of forming a slurry of translucent alumina (α-alumina), a step of forming a molded body of translucent alumina from the slurry, and firing the molded body to transmit light. Forming a light alumina sintered body.

  As a molding method of translucent alumina, a slip casting method, a centrifugal casting method, an extrusion molding method, a press molding method, a waste mud casting method (a mud casting method), and the like are known. In the sludge casting method, a gypsum mold is filled with a slurry containing alumina and held for a predetermined time. The water content of the slurry is absorbed by the gypsum, and the solid content of the slurry deposits on the inner surface of the mold. Next, when the mud is removed (removal of the slurry), the slurried slurry remains on the inner surface of the mold. By drying and releasing this, a light-transmitting alumina molded body is obtained.

JP 2006-62906 JP JP 2007-331965 A

  In the manufacture of a ceramic discharge vessel, shrinkage in the firing process, that is, firing shrinkage is a problem. In the case of a ceramic discharge vessel, the firing shrinkage is 14 to 16%. The firing shrinkage rate should be constant, but if it fluctuates, various problems occur. Thus, techniques for controlling fluctuations in the firing shrinkage have been developed.

  Patent Document 1 describes an example of a method for controlling the cracking rate (firing shrinkage rate) of a green sheet used for a multilayer ceramic substrate. Patent Document 2 describes an example of a firing shrinkage rate adjusting step for adjusting the firing shrinkage rate of a ceramic sheet used in a ceramic laminate. Patent Documents 1 and 2 describe a method for adjusting the firing shrinkage rate of the ceramic sheet, but do not describe a method for adjusting the firing shrinkage rate of the ceramic discharge vessel.

  Accordingly, an object of the present invention is to provide a technique for manufacturing a ceramic discharge vessel that can accurately adjust the firing shrinkage rate without causing an adverse effect on the characteristics of the arc tube by a simple method. It is in.

According to the present invention, in a method for manufacturing a ceramic discharge vessel,
A slurry generating step of mixing alumina, an auxiliary agent, and water to generate a slurry;
A binder addition step of adding a binder to the slurry;
Filling the slurry added with the binder into a gypsum mold, holding for a predetermined time, drying, releasing, forming a molded body,
A pre-baking step of pre-baking the molded body at a relatively low temperature;
A main firing step of firing the temporary fired body formed in the temporary firing step at a high temperature of 1600 ° C. or higher;
Have
The binder adding step includes a step of obtaining a binder content corresponding to a desired firing shrinkage rate from a calibration curve indicating a relationship between a binder content rate and firing shrinkage rate obtained in advance.

  According to the present invention, in the method for manufacturing a ceramic discharge vessel, the calibration curve may be obtained for each alumina production lot.

  According to the present invention, in the method for manufacturing the ceramic discharge vessel, the binder solid content ratio relative to the total solid content in the slurry to which the binder is added may be 0.63 to 5.82 wt%.

  According to the present invention, it is possible to provide a technique for manufacturing a ceramic discharge vessel that can accurately adjust the firing shrinkage rate without causing adverse effects on the characteristics of the arc tube by a simple method. .

FIG. 1A is a diagram illustrating an example of a configuration of a ceramic metal halide lamp according to the present embodiment. Drawing 1B is a figure explaining an example of composition of a discharge vessel of a ceramic metal halide lamp concerning this embodiment. FIG. 2 is a diagram for explaining an example of a method for manufacturing a ceramic discharge vessel for a high-pressure discharge lamp according to this embodiment. FIG. 3A is a diagram showing an example of the relationship between the binder content and the firing shrinkage obtained by experiments conducted by the inventors of the present application. FIG. 3B is an explanatory diagram for explaining a step of determining the binder content in the method for manufacturing a discharge vessel for a ceramic metal halide lamp according to the present invention.

  Hereinafter, embodiments according to the present invention will be described in detail with reference to the accompanying drawings. In the drawings, the same elements are denoted by the same reference numerals, and redundant description is omitted.

  An example of a ceramic metal halide lamp according to the present embodiment will be described with reference to FIG. 1A. The ceramic metal halide lamp 100 includes a translucent outer tube 111, an end cap 112, and a ceramic discharge vessel 130 disposed substantially in the center of the translucent outer tube 111. The inside of the translucent outer tube 111 is maintained in a high vacuum at a pressure of 10 Pa or less. The ceramic metal halide lamp 100 of this embodiment is mounted vertically with the base 112 facing upward as shown.

  A translucent sleeve 108 is provided around the discharge vessel 130, and a metal frame 109 is provided outside thereof. A starter 110 is provided on the upper side of the discharge vessel 130. A getter 113 is attached to the upper end of the frame 109.

  The frame 109 is connected to the lower end mounting support plate 114 and the upper end stem 115 lead-in line, thereby fixing the position. The frame 109 serves not only as a position fixing member but also as a member for electrical connection, and supplies power from an external power supply system (not shown) to the discharge vessel 130 via an introduction line of the stem 115.

  The structure of the discharge vessel 130 will be described with reference to FIG. 1B. The discharge vessel 130 has a central light emitting portion 130C and narrow tube portions 130A and 130B at both ends thereof. Current introduction bodies 120a and 120b are mounted on the thin tube portions 130A and 130B, respectively. The current introduction bodies 120 a and 120 b include a tungsten electrode 123, a current supply body 122, and a lead wire 121. The tungsten electrode 123 is disposed in the light emitting unit 130 </ b> C of the discharge vessel 130. The current supply body 122 includes a halogen-resistant intermediate material 122a and a conductive cermet rod 122b.

  The lead wire 121 is connected to the tip of the conductive cermet rod 122b. The connecting portion between the lead wire 121 and the conductive cermet rod 122b is surrounded by a reinforcing member 131. The lead wire 121 protrudes from both ends of the thin tube portions 130A and 130B.

  Inside the discharge vessel 130, a luminescent material, mercury and an inert gas are enclosed. The inert gas is, for example, a rare gas, but is argon in this embodiment. When the ceramic metal halide lamp is turned on, the luminescent material is heated by the discharge in the discharge vessel 130, and a part thereof is evaporated and excited by the discharge to emit light. The remaining part of the luminescent material is pooled in the liquid phase in the coldest part at the bottom of the discharge vessel 130. A part of the liquid phase luminescent material evaporates, circulates inside the discharge vessel 130 by convection, and returns to the coldest part at the bottom. Such a cycle is repeated while the lamp is on.

  With reference to FIG. 2, the example of the manufacturing method of the ceramic discharge container for high pressure discharge lamps concerning this embodiment is demonstrated. First, in step S101, raw materials are weighed. In this embodiment, alumina powder and an auxiliary agent (magnesium oxide) are used as raw materials. In step S102, a slurry is generated. A raw material in which alumina powder, auxiliary agent, and water are mixed is put into a container, and mixed in a ball mill for 10 hours to produce a slurry. Organic dispersants, plasticizers, solvents and the like may be added. In step S103, a binder is added. Transfer the slurry to another container, add the binder and mix further. Here, the method for determining the binder content will be described in detail later.

  In step S104, the slurry is adjusted. The slurry is passed through a nylon sieve to remove an alumina lump of a certain size or more. Further, bubbles in the slurry are removed by a vacuum defoaming device.

  In step S105, cast molding is performed to obtain a molded body. First, the slurry is filled into a gypsum mold and held for a predetermined time. The water content of the slurry is absorbed by the gypsum, and the solid content of the slurry deposits on the inner surface of the mold. Next, when the mud is removed (removal of the slurry), the slurried slurry remains on the inner surface of the mold. This is dried and released to obtain a molded body.

  In step S106, the molded body is temporarily fired to obtain a temporarily fired body. Pre-baking is performed at a relatively low temperature. For example, the temperature is raised to 950 ° C. over 10 hours and held at that temperature for 30 minutes.

  In step S107, main firing is performed to obtain a sintered body. The main baking is performed at a relatively high temperature. For example, baking is performed at a high temperature of 1600 ° C. or higher. In the present embodiment, two main firings, a primary main firing and a secondary main firing, are performed. The primary main firing is performed in a dry hydrogen atmosphere. Secondary firing is performed in air. Note that the secondary firing may be performed in a wet hydrogen atmosphere or a vacuum atmosphere containing oxygen.

  The reason for performing the main calcination twice is that a low-order oxide is easily generated in alumina only by calcination in a dry hydrogen atmosphere. When the low-order oxide is generated, the sintered body is colored black and the total light transmittance is lowered. However, low-order oxides can be reduced by performing baking in air containing oxygen after baking in a dry hydrogen atmosphere. Therefore, coloring of the sintered body is eliminated and the total light transmittance can be improved.

The concept of the present invention will be described. In the main firing step of Step S107, the calcined body is fired and contracted. Here, the firing shrinkage rate is expressed by the following equation.
Firing shrinkage rate = (L ₀ −L) / L ₀
L ₀ is the total length of the temporarily fired body obtained in step S106 (corresponding to the distance between the outer ends of the narrow tube portions 130A and 130B at both ends). L is the total length of the sintered body obtained in step S107. When the firing shrinkage ratio fluctuates greatly, it is necessary to replace the gypsum mold used in the casting molding in step S105. However, this work is a waste of process and time. Therefore, it is preferable that the firing shrinkage rate is always constant.

  In general, it is considered that the cause of firing shrinkage is the binder. The binder disappears by the preliminary firing, and a large number of minute cavities are generated. In the main firing, it is considered that these minute cavities disappear and firing shrinkage occurs in the volume corresponding to the voids. In addition, when adding an organic dispersing agent, a plasticizer, etc. other than a binder, it is thought that these additives also contribute to baking shrinkage. However, in this embodiment, since the additive is sufficiently smaller than the binder, it may not be considered.

  If the binder content is constant, the firing shrinkage should not fluctuate. However, even if the binder content is constant, the firing shrinkage actually varies. Note that there are firing conditions and the like that affect the fluctuation of the firing shrinkage rate, and these are assumed to be constant.

  Next, factors that cause the firing shrinkage to fluctuate will be considered. The inventors of the present application have focused on alumina powder. In the discharge vessel manufacturing process, it is known that the firing shrinkage varies when the alumina powder manufacturing lot is different, even if the components and composition of the alumina powder are the same. This is considered to be due to the fact that different production lots have different alumina particle sizes, particle size distributions, and the like.

  The inventor of the present application has intensively studied means for suppressing fluctuations in the firing shrinkage rate. In other words, the inventors have intensively studied measures that can suppress fluctuations in the firing shrinkage rate even when the production lots of alumina powder are different. The inventor of the present application focused on the binder content as a parameter for suppressing fluctuations in the firing shrinkage rate. Below, the experiment which the inventor of this application performed is demonstrated.

  FIG. 3A shows the results of an experiment conducted by the inventors of the present application. The inventor of the present application measured the baking shrinkage rate by changing the binder content. A commercially available acrylic resin binder was used as the binder. Organic dispersants, plasticizers, etc. other than the binder are constant. The horizontal axis in FIG. 3 is the binder content (wt%) of the slurry, and the vertical axis is the firing shrinkage (%).

  The relationship between binder content and firing shrinkage was measured for two alumina lots. From the results of this experiment, it can be seen that when the binder content is increased, the firing shrinkage rate increases substantially linearly. Hereinafter, this graph is referred to as a calibration curve. The calibration curve is different for each alumina lot. Here, although the calibration curve was calculated | required about two alumina lots, a calibration curve is previously calculated | required about all the alumina lots used in the manufacturing process of the ceramic discharge containers for high pressure discharge lamps. Thereby, even if the production lot of the alumina powder as a raw material changes, the binder content for always obtaining a desired firing shrinkage rate can be obtained. Once the binder content is obtained, the amount of binder added can be calculated.

  With reference to FIG. 3B, the example of the method of determining the binder content rate by this embodiment is demonstrated. The inventor of the present application previously obtained a calibration curve for each of the alumina lots used for manufacturing the discharge vessel. Here, calibration curves were obtained for three lots of alumina lots A, B, and C. As shown in the figure, the calibration curves were all straight lines. The solid line is the calibration curve for alumina lot A, the dashed line is the calibration curve for alumina lot B, and the dashed line is the calibration curve for alumina lot C. If the desired firing shrinkage value is given, the binder content of the slurry can be read from these calibration curves.

  For example, a desired firing shrinkage value is y1. When the slurry is prepared using alumina lot A, the binder content is x1, when the slurry is prepared using alumina lot B, the binder content is x2, and when the slurry is prepared using alumina lot C. The binder content is x3. Once the binder content is obtained, the amount of binder added can be calculated. According to this embodiment, even if the alumina lot changes, the desired firing shrinkage can be maintained by changing the binder content.

  The binder content (wt%) on the horizontal axis in FIGS. 3A and 3B is the weight percentage of the binder with respect to the total weight of the slurry after the addition of the binder in step S103. However, the commercially available binder used in the above experiments was in the form of a slurry having a solid content of 40 wt% and a moisture content of 60 wt%. Accordingly, the binder solid content (wt%) is smaller than the binder content (wt%). In order to convert the binder content (wt%) into the binder solid content (wt%), the binder content (wt%) may be multiplied by 0.4. For example, when the binder content (wt%) is x and the binder solid content (wt%) is B1, B1 = 0.4x (wt%).

Next, the binder solid content ratio (wt%) to the total solid content of the slurry after the binder is added is determined. When the binder content (wt%) is x, the weight percentage of the remaining slurry is (100−x). The solid content of the slurry is alumina. The content of alumina in the slurry generated in step S102 was 64 wt%. Therefore, the weight percentage of alumina in the slurry after addition of the binder is (100−x) × 0.64. The total solid content of the slurry after the binder addition is alumina and binder solid content, which is (100−x) × 0.64 + 0.4x. When the binder solid content ratio (wt%) to the total solid content of the slurry after adding the binder is B2, B2 is represented by the following equation (1).
B2 = 0.4x ÷ {(100−x) × 0.64 + 0.4x} × 100 (wt%): Formula 1

  From the above experimental results, it was found that if the binder content is in the range of 1 to 9%, the sintered ceramic body after the main firing has no problem in characteristics as a discharge vessel. When the binder content of 1 to 9% is converted into the binder solid content ratio with respect to the total solid content using the above-described formula 1, it becomes 0.63 to 5.82 wt%. Therefore, when the range of the binder solid content ratio is 0.63 to 5.82 wt%, it can be said that the sintered ceramic body after the main firing does not cause a problem in characteristics as a discharge vessel.

  As mentioned above, although manufacture of the discharge vessel made from ceramics concerning this embodiment was explained, these are illustrations and do not restrict the range of the present invention. Additions, deletions, changes, improvements, and the like that can be easily made by those skilled in the art to the present embodiment are within the scope of the present invention. The technical scope of the present invention is defined by the appended claims.

DESCRIPTION OF SYMBOLS 100 ... Ceramic metal halide lamp, 108 ... Translucent sleeve, 109 ... Frame, 110 ... Starter, 111 ... Translucent outer tube, 112 ... Base, 113 ... Getter, 114 ... Mount support plate, 115 ... Stem, 120a, 120b ... Current introducing member, 121 ... Lead wire, 122 ... Power supply conductor, 122a ... Halogen resistant intermediate material, 122b ... Conductive cermet, 123 ... Tungsten electrode, 130 ... Discharge vessel, 130C ... Light emitting part, 130A, 130B ... Narrow tube part, 131 ... Reinforcing material

Claims (3)

In the method for manufacturing a ceramic discharge vessel,
A slurry generating step of mixing alumina, an auxiliary agent, and water to generate a slurry;
A binder addition step of adding a binder to the slurry;
Filling the slurry added with the binder into a gypsum mold, holding for a predetermined time, drying, releasing, forming a molded body,
A pre-baking step of pre-baking the molded body at a relatively low temperature;
A main firing step of firing the temporary fired body formed in the temporary firing step at a high temperature of 1600 ° C. or higher;
Have
The binder adding step includes a step of obtaining a binder content corresponding to a desired firing shrinkage rate from a calibration curve indicating a relationship between a binder content rate and a firing shrinkage rate obtained in advance. In the manufacturing method of the discharge vessel made of ceramics according to claim 1,
The method for producing a discharge vessel, wherein the calibration curve is obtained for each production lot of alumina. In the manufacturing method of the discharge vessel made of ceramics according to claim 1 or 2,
The method for producing a discharge vessel, wherein the binder solid content ratio to the total solid content in the slurry to which the binder is added is 0.63 to 5.82 wt%.

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